A tire generally comprises a tread forming a surface of revolution about an axis of rotation of the tire. The tread includes in particular a design for providing the tire with good grip.
Wear of the tread causes the design to wear away, thereby reducing the grip performance of the tire.
In the particular circumstance of a tire for a vehicle of the heavy goods type, it is known to form channels in the mass of rubber forming the tread specifically for the purpose of limiting the loss of tire grip as the tread wears away. Wearing down the rubber of the tread causes the channels to become flush in the surface of the tread. The flush channels then form grooves that serve to replace at least in part the initial design of the tread that has been worn away.
It is known to fabricate a tire by vulcanizing an unvulcanized blank in a mold comprising:                top and bottom axial members (also known as “shells”), each carrying a surface for molding a sidewall of the tire; and        radial segments, each carrying a surface for molding the tire tread (which molding surface is also referred to as a “liner”).        
At least one sidewall-molding member is movable axially between a sidewall-molding position and a tire-unmolding position, in particular so as to enable said tire to be extracted.
In order to form the channels mentioned above, the mold generally includes top and bottom sets of channel-molding members, as described for example in JP 2002 307442A. Each set of channel-molding members is axially movable between a channel-molding position and a channel-unmolding position.
In the mold described in JP 2002 307442A, the top and bottom sets of channel-molding members are secured respectively to the top and bottom axial members. Thus, moving the axial members between their sidewall-molding positions and their tire-unmolding positions causes the sets of channel-molding members to move between their channel-molding and channel-unmolding positions.
The mold described in JP 2002 307442A further includes means for guiding the channel-molding members in the mold. These guide means comprise female slides provided in the radial segments of the mold.
Each mold segment described in JP 2002 307442A comprises top and bottom halves connected respectively to the top and bottom axial sidewall-molding members by means that allow for axial relative movement between the segment halves and the axial members for molding the sidewalls.
The female slides for guiding the top set of channel-molding members are arranged in the top halves of the segments, and the female slides for guiding the bottom set of channel-molding members are arranged in the bottom halves of the segments.
The axial relative movement of each segment half relative to the corresponding axial member for molding a sidewall is limited so as to prevent the channel-molding members from disengaging from their guiding slides when the channel-molding members are moved from their molding positions to their unmolding positions.
Thus, when the mold described in JP 2002 307442A is open, the axial movement of the sidewall-molding axial members enables the vulcanized tire to be withdrawn from the channel-molding members without disengaging the channel-molding members from the guide slides.
Nevertheless, in order to open the mold, it is necessary to move each sidewall-molding axial member together with the radial segment path to which it is connected. In addition, when closing the mold, it is necessary to take care that the junction between the radial segment halves is properly sealed. This makes the mold relatively complex to handle.